1. Field of the Invention
The present invention relates to monolithic ceramic electronic components, and particularly to a technique to prevent structural defects caused by internal stress from occurring in a monolithic ceramic electronic component.
2. Description of the Related Art
Monolithic ceramic electronic components include ceramic laminates including stacked ceramic layers and internal electrodes extending therebetween. During manufacture of the monolithic ceramic electronic components, each ceramic laminate is prepared using a firing step. In the firing step, the ceramic layers and the internal electrodes are co-fired. Structural defects, such as cracks, may occur in the ceramic laminate in the firing step because of the difference in sintering shrinkage between a ceramic material included in the ceramic layers and a metal included in the internal electrodes. This phenomenon is described below in detail with reference to a monolithic ceramic capacitor.
The monolithic ceramic capacitor includes ceramic layers made of BaTiO3 and internal electrodes made of Ni. As compared to BaTiO3, Ni has a greater thermal shrinkage. During cooling of the fired ceramic layers and internal electrodes to room temperature, the ceramic layers shrink at a relatively low rate and the internal electrodes shrink at a relatively high rate.
The ceramic layers and the internal electrodes are combined with each other and therefore cannot shrink separately. Thus, the shrinkage of each ceramic layer is greater than the intrinsic shrinkage thereof. This produces a compression stress on the ceramic layer. On the other hand, the shrinkage of each internal electrode is less than the intrinsic shrinkage thereof. This produces a tensile stress on the internal electrode. The compression and tensile stresses remain in the ceramic laminate as internal stresses which tend to cause cracks over time.
The size reduction and performance enhancement of electronic devices require that monolithic ceramic electronic components have a smaller size and an increased performance. For example, monolithic ceramic capacitors must include an increased number of thin ceramic layers and thin internal electrodes so as to have a smaller size and a greater capacitance.
The increase in the number of the ceramic layers and the internal electrodes tends to increase the internal stresses in the ceramic laminates. The internal stresses are likely to be concentrated at the boundaries between the ceramic layers and the internal electrodes, that is, at peripheral portions of the internal electrodes.
FIGS. 9A and 9B are sectional views of a capacitor array 1 disclosed in Japanese Unexamined Patent Application Publication No. 6-314634. The capacitor array 1 is an example of a conventional monolithic ceramic electronic component related to the present invention. FIGS. 9A and 9B are taken along different sections of the monolithic ceramic electronic component.
The capacitor array 1 includes a ceramic laminate 5 having a substantially rectangular parallelepiped shape. The ceramic laminate 5 includes a plurality of stacked ceramic layers 2 and has a first principal surface (not shown), a second principal surface (not shown) opposed to the first principal surface, a first side surface 3, and a second side surface 4 opposed to the first side surface surface 3. Four first external terminal electrodes 6 are arranged on the first side surface 3 of the ceramic laminate 5. Four second external terminal electrodes 7 are arranged on the second side surface 4 of the ceramic laminate 5.
The ceramic laminate 5 includes four first internal electrodes 8 each electrically connected to one of the four first external terminal electrodes 6 as shown in FIG. 9A and four second internal electrodes 9 each electrically connected to one of the four second external terminal electrodes 7 as shown in FIG. 9B.
The first internal electrodes 8 include first opposed portions 10 which are opposed to the second internal electrodes 9 with one of the ceramic layers 2 disposed therebetween and include first lead portions 11 which extend from the first opposed portions 10 to the first side surface 3 and which are electrically connected to the first external terminal electrodes 6. The second internal electrodes 9 include second opposed portions 12 which are opposed to the first internal electrodes 8 with one of the ceramic layers 2 disposed therebetween and second lead portions 13 which extend from the second opposed portions 12 to the second side surface 4 and which are electrically connected to the second external terminal electrodes 7. The widths of the first lead portions 11 and the second lead portions 13 are less than the first opposed portions 10 and the second opposed portions 12, respectively.
FIG. 10 is a partial enlarged view of the ceramic laminate 5 shown in FIG. 9A. FIG. 10 shows a portion of one of the first opposed portions 10 and one of the second lead portions 13 that is indicated by broken lines. The second opposed portions 12 overlap the first opposed portions 10.
As shown in FIG. 10, the first opposed portions 10 have first end portions 14 located on the side opposite to the first lead portions 11 and the second opposed portions 12 have second end portions 15 located on the side adjacent to the second lead portions 13. The first end portions 14 overlap with the second end portions 15. Thus, internal stresses are likely to be concentrated at the first and second end portions 14 and 15. The second lead portions 13 have first side portions 16 and second portions 17, at which internal stresses are likely to be concentrated. These elements cause internal stresses to be primarily concentrated at the corners 18 of the bases of the second lead portions 13, the corners 18 being indicated by circles in FIG. 10. Thus, cracks are likely to occur at the corners 18.